Apparatus for determining flatness deviation in sheet or strip

ABSTRACT

Continuous monitoring of the shape of cold rolled strip is provided by passing the strip, under tension, over a roll. A line of sensors on the roll surface measures the longitudinal stress distribution across the width of the strip indicating the location, magnitude and type of flatness defect which will appear when the tension is removed.

United States Patent Atkins et al.

[451 Sept. 5, 1972 [54] APPARATUS FOR DETERMINING FLATNESS DEVIATION INSHEET OR STRIP legheny County, both of Pa.

[73] Assignee: United States Steel Corporation,

[22] Filed: Dec. 11, 1969 [21] Appl. No.: 884,087

3,324,695 6/ 1967 Sivilotti ..72/12 3,334,508 8/ 1967 Martin ..73/1443,442,104 1969 Misaka et al. ..73/ 144 3,481,194 12/ 1969 Sivilotti..73/144 3,499,306 3/1970 Pearson ..73/159 3,413,846 12/1968 Flinth..73/141 3,526,l 14 9/1970 Wistreich ..72/9 3,554,025 1/ 1971 Andeissonet al. ..73/ 144 Primary ExaminerRichard C. Queisser AssistantExaminer-Herbert Goldstein Attorney-Rea C. Helm [57] ABSTRACT (g1Continuous monitoring of the Shape of cold rolled strip is p g the punder tension of over a roll. A line of sensors on the roll Surfacesures the longitudinal stress distribution across the [56] Referencescued width of the strip indicating the location, magnitude UNITED STATESPATENTS and type of flatness defect which will appear when the tensionis removed. 2,674,127 4/1954 Garrett et a1. ..73/159 2,809,519 /1970Kaestner ..73/159 3 Claims, 10 Drawing Figures III l8 1 1a 34 32 H I/6-- l6 2e 2;, I 20 @222; 3a 9 H To To EZZ/a; Display Un/f Z PATENTEDSEP5:912

SHEET 1 OF 3 DISPLAY UNIT FIG 2 m. mum I4 m? mam 8 0 TE m w 4 mm n TY .LMN D w m m m A m a m m w w 8 m o n x rm wnw 1 F m, m M0 6 0 2 v a TAttorney PATENTED E 5 SHEET 2 OF 3 M in I/T/T/T fT/T/T fW/Tn EDGE T EIVS/0N QMRTER POINT T E IVS/0N CENTER TE IVS/0N QUARTER POINT T E IVS/0NE 06E TE IVS/ON FIG. 3

ANTHONY a. ATKINS,

BAY E ESTES, m

' & RICHARD L. RENNER A g M PATENTEDsEP 51912 3.688.571 sum sur 3 FIG.5A H6. 55

AVERAGE TENS/LE DISTRIBUTION ACTUAL STRESS INCREASING DISTRIBUTION TENSION LOOSE E0655 AVERAGE TENS/LE DISTRIBUTION ACTUAL smsss [Ne/7545mmDISTRIBUTION TENS/0N FIG. 6.4

TIGHT E0655 MUL TICHAIVIVEL 0500mm U D D D AVERAGE D D D D 5 5 ETC ONEOIVE REVOLUTION REVOLUTION FIG: 8 INVE'IV TORS OSCILLOSCOPE ANTHONY G.ATKINS, EA) 5. ESTES, ZZZ a man/m0 L. RENNER 3 D4 AVERAGE 1?, Z M

Attorney APPARATUS FOR DETERMINING FLATNESS DEVIATION IN SHEET OR STRIPThis invention relates to method and apparatus for determining thedeviation from flatness in a sheet or strip and more particularly forcontinuously determining deviations from flatness in cold rolled stripsteel as it is being rolled under tension and passing over a bridle rollunder tension to a coiler.

When a steel strip is subjected to non-uniform deformation conditions inthe roll bite internal stresses are created within the strip as longerover-rolled material attempts to line up with shorter under-rolledportions. In heavier gage strip, the stresses may not be of sufficientmagnitude to buckle the strip but in the lighter gages of tinplate andfoil it is more likely the stresses will relieve themselves by bucklingthe strip on exit from the mill. The extend of the defect depends on thethickness of the strip and the amount of non-uniform deformation.

Surface flatness of strip can be determined by mechanical measurementsbut this is most difficult with thin material, particularly if thematerial is under tension. In principal, specular reflection could beused to measure shape but the interpretation of results would becomplicated and of questionable reliability. Visual observation of stripflatness is unreliable and almost impossible on a high speed productionmill with the strip under high tension and masked by flow of lubricantand coolant. Thus, there is no method that we are aware of to assess thequality of flatness in a strip during rolling.

According to our invention, a line of load cells is mounted inside thebridle roll to measure the strip tension across the width of the strip.The distribution of the tension across the width of the strip thenbecomes a measure of flatness as to magnitude, location and type ofdeviation from flatness.

It is, therefore, an object of our invention to provide a method formonitoring the flatness of strip as it passes over a roll under tension.

Another object is to provide a method for determining the magnitude offlatness and deviation from flatness of strip as it passes over a rollunder tension.

Still another object is to provide apparatus for continuouslydetermining the flatness and deviation from flatness of strip as itpasses over a roll under tension.

A still further object is to provide apparatus for determining thelocation, magnitude and type of deviation from flatness of strip as itpasses over a roll under tension.

A still further object is to provide such apparatus for determiningflatness regardless of the level of tension in the strip.

These and other objects will become more apparent after referring to thefollowing specification and drawings, in which:

FIG. 1 is an isometric diagrammatic view of cold rolling with the bridleroll of our invention;

FIG. 2 is a schematic sectional view through the center of the bridlerolling together with connections to slip rings, timer and display unitof our invention;

FIG. 3 is a partial sectional view along line III-III of FIG. 2 showingthe load cell and transfer pin arrangement;

FIG. 4 is a chart showing a typical signal display for a strip withcenter buckles on a five-pen strip chart recorder;

FIGS. 5A and 5B illustrate a strip with loose edges and the longitudinalstress distribution;

FIGS. 6A and 6B illustrate a strip with tight edges and the longitudinalstress distribution;

FIG. 7 illustrates a multi-point chart recorder readout of loose edges;and

FIG. 8 illustrates an oscilloscope readout of tight edges.

Referring now to the drawings, and particularly to FIG. 1, referencenumeral 2 indicates an uncoiler from which a strip S is unwound. Thestrip S passes over and around entry bridle rolls 4 through work rolls6, over and around exit bridle roll 8, over and around bridle roll 10and is coiled on recoiler 12. This is a typical arrangement of a coldroll steel strip mill in which the strip S is under tension between thebridle rolls.

Referring now to FIG. 2, tension measuring exit bridle roll 8 isgenerally hollow and has five compression type load cells 14 mountedinside roll 8. The load cells may be Model 3108- manufactured by LebowAssociates, Inc., Oak Park, Mich. Other types of transducers may be usedin place of the load cells. A transfer pin 16 is associated with eachload cell 14 and extends from the load cell 14 through a hole 18 in theshell of roll 8, protruding beyond the surface of roll 8 very slightlyto contact the underside of a thin rubber sleeve 20 covering roll 8.Strip S will just contact the projection in sleeve 20 caused by transferpin 16 as shown in FIG. 3. The load cells 14 and transfer pins 16 arearranged so that holes 18 are in a straight line across the surface ofthe roll 8 parallel to its axis.

Roll 8 has a shaft 22 with a timer assembly 24 on one end and a slipring assembly 26 on the other end. Timer assembly 24 has a set ofcontacts 28 which are closed by a cam 30 when pins 16 arrive at point Awhere strip S makes contact with roll 8 until pins 16 arrive at point Bwhere strip S leaves contact with roll 8 as shown in FIG. 3.

Slip ring assembly 26 has a pair of input rings 32 with inputconnections to each cell 14 but for the purposes of illustration, aconnection to only one load cell 14 is shown. A pair of output sliprings 34 is connected to each load cell 14 but for the purposes ofillustration, the rings and connections to only one load cell 14 isshown. A pair of slip ring brushes 36 connects power to load cells 14from a suitable power source 38 through connections 40. Another pair ofslip ring brushes 42 connects the output from load cells 14 to a displayunit 44 through connections 46. Contacts 28 are connected to displayunit 44 through connections 48. Display unit 44 is a five-pen stripchart recorder such as manufactured by Brush Instrument Division ofClevite Corporation, Cleveland, Ohio, which records the signals fromload cell 14 during the time when contacts 28 are closed. Journal boxes50 of shaft 22 have load cells 52 connected to display unit 44 byconnections 54.

Under optimal conditions, internal stresses are evenly distributedthroughout the strip and the normal reaction tensile loading force ofstrip S on roll 8 is carried evenly distributed across the face of roll8. The strip will remain flat when tension is removed. If the strip isrolled so as to develop uneven internal stresses, such as loose orover-rolled sections, those sections will carry less of the normalreaction tensile loading on the exit bridle roll 8 than tight orunder-rolled sections.

Thus, the loose and over-rolled wavy and buckled edges of a strip shownin FIG. 5A resuit in the uneven internal stress distribution and theuneven tensile distribution on the exit bridle shown in FIG. 58, whilethe tight and under-rolled edges of the strip shown in FIG. 6A result inthe stress distribution of the exit bridle roll shown in FIG. 6B.

As the strip passes over pins 16 the differences in tensile loadingsacross the face of roll 8 produce different signals which are recordedon display unit 44. FIG. 4 shows such signals for three revolutions ofroll 8 where the differences between the signals indicate that the striphas very low tensile loadings in the center as compared to the edges andthe edges have slightly different tensile loadings.

Thus the differences between signals from load cells 14 indicate therelative degree of flatness of the strip S as it passes over roll 8.Whether or not the strip will in fact have buckles will depend on thethickness of the strip and the amount of nonuniform deformation.

While the differences between signals from load cells 14 indicate thatthere may be a departure from flatness, this difference by itself doesnot indicate the extent of the departure and therefore does not indicatewhether or not the departure from flatness is within tolerance limits.This is determined by first finding the total tensile loading from loadcells 52 and then determining the average load cell tensile load fromthe contact areas of pins 16 as compared to the total tensile load area,the roll face area from point A to point B of FIG. 3. The average couldalso be determined by averaging all the load cell signals sent todisplay unit 44. The average tension is shown for each of the fiverecordings in FIG. 4. This could show, for example, that the edges andcenter are out of tolerance while the quarter points are in tolerance.

FIG. 7 shows the flatness readout where display unit 44 is a multi-pointchart recorder which records the peaks or rms values of the signals fromload cells 14. FIG. 8 shows the flatness readout where display unit 44is an oscilloscope in which the sweep and afterglow provide a continuousflatness pattern. Obviously the flatness deviation signals may also beused as control signals for the strip production equipment byconnections 56 from display unit 44 to adjust rolls 6. These readoutsrequire additional conventional circuitry in display unit 44 todetermine and display averages and tolerance limits so that comparisonscan be made.

Timer cam 30 has been indicated as closing points 28 from point A topoint B, thereby defining the degree of wrap of strip S around the roll8. Contacts 28 control the length of the signals in display unit 44which may be wide as shown in FIG. 4 or the signals may be narrow (withappropriate adjustments to average determination) by a different camsurface to provide the signal shown in FlGS. 7 or 8.

While five load cells have been shown and described, ideally acontinuous tensile determination would be made across the width of thestrip instead of at discrete locations. More than one line of load cellsmay be placed on a bridle roll.

The tension required in the strip should be of suffcient magnitude toprovide some tensile loading throughout the width of the strip so thatthere will be a signal from the load cell at the least strained sectionof strip. This method is particularly useful when the high exit tensionin a cold rolled strip mill masks any visual observation of flatnessdeviation. The relative flatness determination and the magnitude of thedeviation from flatness are therefore independent of the strip tension.

This method of flatness determination is obviously useful for any typeof metal or plastic material, either in the form of sheet or strip, thatmay develop internal stresses in forming and to which tension may beapplied and the normal reaction force caused by the tension measured ata location where the material changes longitudinal direction.

While the apparatus shown and described uses an electrical signalsystem, fluid systems using for example oil or water, could also beused.

We claim:

1. Apparatus for determining the flatness characteristics of alongitudinally moving strip under sufiicient tension to maintain saidstrip substantially flat which comprises a roll with its axisperpendicular to the direction of travel of said strip over which saidstrip passes with an angle of wrap sufficient to provide a measurablereaction force perpendicular to said strip against said roll at theleast strained portion of said strip, a plurality of load cells mountedinside said roll along a line parallel to the roll axis, a plurality oftransfer pins each connected to one of the load cells at one end andterminating slightly beyond the surface of the roll at the other end,said pins being adapted to transfer the reaction force of the strip onthe end area of each pin to the associated load cell when the rotationof the roll causes a row of pin ends to contact the strip, said loadcells providing negligible displacement under load, and means connectedto the load cells for displaying the output of the load cells.

2. Apparatus according to claim 1 in which said roll is a bridle roll ina cold roll steel strip mill.

3. Apparatus according to claim 1 which includes a relatively thinresilient covering over said roll between the strip and the roll faceand the roll face ends of said transfer pins.

1. Apparatus for determining the flatness characteristics of alongitudinally moving strip under sufficient tension to maintain saidstrip substantially flat which comprises a roll with its axisperpendicular to the direction of travel of said strip over which saidstrip passes with an angle of wrap sufficient to provide a measurablereaction force perpendicular to said strip against said roll at theleast strained portion of said strip, a plurality of load cells mountedinside said roll along a line parallel to the roll axis, a plurality oftransfer pins each connected to one of the load cells at one end andterminating slightly beyond the surface of the roll at the other end,said pins being adapted to transfer the reaction force of the strip onthe end area of each pin to the associated load cell when the rotationof the roll causes a row of pin ends to contact the strip, said loadcells providing negligible displacement under load, and means connectedto the load cells for displaying the output of the load cells. 2.Apparatus according to claim 1 in which said roll is a bridle roll in acold roll steel strip mill.
 3. Apparatus according to claim 1 whichincludes a relatively thin resilient covering over said roll between thestrip and the roll face and the roll face ends of said transfer pins.